Tantalum (Ta) thin films are widely used in manufacturing of semiconductor and micro-electromechanical systems (MEMS). For example, in semiconductor integrated circuit manufacturing, tantalum may be used as a diffusion barrier between copper and silicon. Tantalum may also be used as a gate electrode in metal oxide semiconductor field effect transistor (MOSFET) devices. Tantalum may also be used to absorb X-rays in X-ray masks. In thermal inkjet MEMS such as a printhead, tantalum is used as a protective overcoat on the resistor and other substrate layers to protect the underlying layers from damage caused by cavitation from the collapsing ink bubbles. The tantalum layer also protects the underlying layers of a printhead from chemical reactions with the ink.
The metastable tetragonal phase of tantalum, known as the beta-phase or “beta-tantalum” is typically used in the manufacture of thermal inkjet devices. This beta-tantalum layer is brittle and becomes unstable as temperatures increase. Above 300° C., beta-tantalum converts to the body-centered-cubic (bcc) alpha-phase or “alpha-tantalum.” Alpha-tantalum is the bulk equilibrium or stable-phase of tantalum. It is desired to form stable, compressive alpha-tantalum films on fluid ejection devices. Such compressive alpha-tantalum films may increase the useful life of such devices by resistance to peeling, blistering or delamination from the substrate.